Heretofore, as this type of control circuit of transportable crusher, there has been proposed the control circuit of the transportable crusher shown in FIG. 14 (see Japanese Utility Model Laid-open No. 6-81641/1994).
In FIG. 14, a variable displacement left-side traveling hydraulic pump 101, a variable displacement right-side traveling hydraulic pump 102, and a fixed displacement controlling hydraulic pump 103 are driven by an engine (not shown) mounted in the transportable crusher.
A hydraulic fluid discharged from the left-side traveling hydraulic pump 101 flows into a P port of a left-side traveling switching control valve 104 (hereinafter, referred to as left-side control valve 104). This hydraulic fluid is supplied to a hydraulic motor 105 in a hydraulically drivable type forwardly reversely rotatable left-side traveling truck connected to an A port and a B port of the left-side control valve 104.
The hydraulic fluid discharged from the right-side traveling hydraulic pump 102 flows into the P port of a right-side traveling switching control valve 106 (hereinafter, referred to as a right-side control valve 106). This hydraulic fluid is supplied to a hydraulic motor 107 in a hydraulically drivable type forwardly reversely rotatable right-side traveling truck connected to the A port and the B port of the right-side control valve 106.
When the left-side control valve 104 is positioned at its neutral position S, the left-side control valve 104 is "an open-center type six-port and three-position pilot hydraulic control valve" which is communicated with the P port and an N port so as to bypass a flow. The left-side control valve 104 and the right-side control valve 106 have the same structure.
When each of the left-side control valve 104 and the right-side control valve 106 is positioned at its neutral position S, the hydraulic fluid discharged from the left-side traveling hydraulic pump 101 and the hydraulic fluid discharged from the right-side traveling hydraulic pump 102 flow out of the N ports. After that time, the hydraulic fluids are joined to each other and flow into the P port of a hydraulic control valve 108 for the crusher. This hydraulic fluid is supplied to a hydraulic motor 109 for the crusher connected to the A port and the B port of the hydraulic control valve 108 for the crusher. Two relief valves 110, 110 for the crusher are arranged in this control circuit in such a manner that a supplied hydraulic pressure is not a predetermined value or higher during a forward-and-reverse rotation of the hydraulic motor 109 for the crusher.
The hydraulic control valve 108 for the crusher also has the same structure as the left-side control valve 104 and the right-side control valve 106. When the hydraulic control valve 108 for the crusher is positioned at its neutral position S, its P port and its N port are communicated with each other so as to drain the hydraulic fluid into a tank 123.
When the left-side control valve 104 and the right-side control valve 106 are switching-controlled to their first switching position F so that the respective P port is communicated with the respective A port, the left-side hydraulic motor 105 and the right-side hydraulic motor 107 are rotated forwardly. On the other hand, when the left-side control valve 104 and the right-side control valve 106 are switching-controlled to their second switching position R so that the respective P port is communicated with the respective B port, the left-side hydraulic motor 105 and the right-side hydraulic motor 107 are rotated in reverse.
When the left-side hydraulic motor 105 and the right-side hydraulic motor 107 are driven, that is, when the hydraulic pressure from the respective P port is supplied to either the respective A port or the respective B port in the left-side control valve 104 and the right-side control valve 106, the respective N port for supplying the hydraulic pressure to the hydraulic control valve 108 for the crusher is always blocked. Thus, the hydraulic motor 109 for the crusher is not driven.
On the other hand, when the left-side control valve 104 and the right-side control valve 106 are positioned at their respective neutral position S, hydraulic pressure is supplied from the respective N port. The hydraulic motor 109 for the crusher is driven in accordance with the thus joined hydraulic pressure.
The controlling hydraulic pump 103 supplies hydraulic pressure to a control hydraulic line 111 which is connected to the left-side control valve 104, the right-side control valve 106, and the hydraulic control valve 108 for the crusher. The controlling hydraulic pump 103 also supplies the hydraulic pressure to hydraulic lines 112, 113, and 114, which are connected to the hydraulic motors for attached devices, such as a discharge conveyor, a magnetic separator, and a conveyor derricking device, by a shunt circuit 115.
The shunt circuit 115 is shunted into two systems by a first priority valve 116 on the discharge side of the controlling hydraulic pump 103. One outlet side port of the first priority valve 116 is connected to the hydraulic line 112, which is connected to the hydraulic motor for the discharge conveyor and to a first relief valve 117. The other outlet side port of the first priority valve 116 is connected to an inlet side port of a second priority valve 118.
Similarly, the outlet side port of the second priority valve 118 is connected to the hydraulic line 113 which is connected to the hydraulic motor for the magnetic separator and to a second relief valve 119. The other outlet side port of the second priority valve 118 is connected to the inlet side port of a third priority valve 120.
In a last step, one outlet side port of the third priority valve 120 is connected to the hydraulic line 114, which is connected to the hydraulic motor for the conveyor derricking device and to a third relief valve 121. The other outlet side port of the third priority valve 120 is held to a predetermined control pressure by a relief valve 122 for the control hydraulic line and is connected to the control hydraulic line 111.
Each hydraulic motor for these attached devices is connected so that the motor requiring the higher hydraulic pressure during an operation can be located in a previous step. The first, second, and third priority valves 116, 118, and 120 are constructed so that they can be shunted at a flow rate distribution ratio of as high as, for example, one to ten. The first, second, and third priority valves 116, 118, and 120 are arranged in accordance with the number of hydraulic motors.
A joined discharge flow rate from the left-side traveling hydraulic pump 101 and the right-side traveling hydraulic pump 102 is supplied to the hydraulic motor 109 for the crusher so that the speed may not be reduced if the load and a load variation become larger.
The hydraulic motors for the discharge conveyor, for the magnetic separator, and for the conveyor derricking device have less displacement and less load variation than the hydraulic motor 109 for the crusher. However, the controlling hydraulic pump 103 for the control hydraulic line 111 and for the hydraulic lines 112, 113, and 114 for the attached devices is a fixed displacement type having a large pump displacement. The controlling hydraulic pump 103 includes the shunt circuit 115 which shunts the excess discharge flow rate. The controlling hydraulic pump 103 is used through the priority valves 116, 118, and 120 of the shunt circuit 115.
Accordingly, the two variable displacement traveling hydraulic pumps 101 and 102, for use with the hydraulic motor 109 for the crusher, and the single fixed displacement controlling hydraulic pump 103, for use with both the control hydraulic line 111 and the attached devices, have no influence on each other, even if the loads of both the pumps are varied. Thus, they can be independently driven.
FIG. 15 shows an example of a prior-art speed control circuit of a hydraulic motor 124 for a feeder. This speed control circuit controls a speed of the hydraulic motor 124 for the feeder in order to select an introduction speed of objects to be crushed in accordance with the size and hardness of the objects to be crushed and the kind of crusher used for crushing the objects.
A speed control of the hydraulic motor 124 for the feeder is accomplished by a bleed-off circuit in which a flow rate regulating valve 125 is inserted between the discharge side of the hydraulic pump 103 and a tank 123. A discharge flow rate Qp of the hydraulic pump 103 is divided into a flow rate Q.sub.M to be supplied to the hydraulic motor 124 for the feeder and a flow rate Q.sub.T to be shunted to the tank 123. The excess flow rate Q.sub.T is regulated by the flow rate regulating valve 125. The flow rate Q.sub.M, alone required for the hydraulic motor 124 for the feeder, is supplied through a switching control valve 126 for the feeder.
On the other hand, the conventional control circuit of the transportable crusher includes the two variable displacement traveling hydraulic pumps 101 and 102. The reason is as follows. When the load of the left-side hydraulic motor 105 is different from that of the right-side hydraulic motor 107, even if the left-side control valve 104 and the right-side control valve 106 have the same stroke, the hydraulic fluid flows into the hydraulic motor having the lower load. Therefore, since the speed of the hydraulic motor having the higher load becomes lower, the transportable crusher cannot travel in a straight line. Thus, the two traveling hydraulic pumps 101 and 102 are disposed so as to ensure straight traveling. However, this complicates the piping system and the control system, and a maintenance check takes a long time, thereby resulting in a high cost.
The left-side control valve 104 and the right-side control valve 106 are the open-center type in which the respective P port and the respective N port are communicated with each other at the neutral position S. Thus, during each half stroke, the hydraulic fluid, set to a predetermined pressure at the P port, is partially drained into the tank 123 via the P port and the N port of the hydraulic control valve 108 for the crusher. If a drain flow rate is high, a power loss of the traveling hydraulic pumps 101 and 102 is caused. If the drain flow rate remains high for a long time, the hydraulic fluid is heated, thereby causing an overheating of the hydraulic circuit. In such a manner, a problem is caused.
When the single fixed displacement controlling hydraulic pump 103, for use in both the control hydraulic line 111 and the hydraulic lines 112, 113, and 114 for the attached devices, is installed, a large pump displacement is required for the total flow rate necessary for these lines.
For example, with regard to the crusher broadly illustrated in FIG. 3, the controlling hydraulic pump 103, having a larger pump displacement, is also required in order to supply the hydraulic fluid to each hydraulically drivable type motor for a feeder 29 for stably supplying the objects to be crushed which are introduced into the hopper for crusher 28, a vibrating screen 32, a plurality of secondary conveyors 33 and 34, etc.
In addition, the shunt circuit 115, having a different predetermined set pressure, is disposed on the discharge side of the controlling hydraulic pump 103. As the number of attached devices is increased as described above, the priority valve and the relief valve for the control hydraulic line, to be mounted to each hydraulic line, must be increased. As a result, the drain flow rate is further increased, thereby resulting in further power loss of the controlling hydraulic pump 103. Since the hydraulic fluid is heated, the hydraulic circuit can become overheated. Since the piping system and the control system are complicated, the maintenance check takes a long time.
Furthermore, assume that the discharge conveyor is overloaded, that is, the objects to be crushed are discharged over a predetermined throughput capacity of the discharge conveyor. At that time, the first relief valve 117, of the hydraulic line 112 connected to the hydraulic motor for the discharge conveyor, is relieved; and thereby the hydraulic motor 109 for the crusher and the feeder are automatically stopped. Although an operator can restart the motor and the feeder after a check of the failure, this is troublesome.
The speed control circuit of the hydraulic motor 124 for the feeder shown in FIG. 15 selects the flow rate Q.sub.M required for the hydraulic motor 124 for the feeder by the flow rate regulating valve 125 and regulates the flow rate Q.sub.T to be shunted to the tank 123. However, when the load and an oil temperature of the hydraulic fluid are varied in accordance with the amount of the objects, to be crushed, on the feeder, the flow rate Q.sub.M is changed and thereby the speed of the hydraulic motor 124 for the feeder is also changed. Disadvantageously, the reduction of the speed of the hydraulic motor 124 for the feeder results in a reduction of crushing efficiency.
According to the circumstances of the load and the oil temperature of the hydraulic fluid, the crusher can be abnormally overloaded. Thus, the objects to be crushed jam the crusher, thereby resulting in an emergency stop. Immediately before the abnormal overload, it is difficult for the operator to regulate the flow rate regulating valve 125. It is also very difficult to remote-control the flow rate regulating valve 125, which is incorporated in the structure of the switching control valve 126 for the feeder.
Even if the load of the hydraulic motor 124 for the feeder is reduced, the jammed objects to be crushed must be removed from the crusher in an emergency-stop status. Therefore, since an automatic restoration is difficult, the operating efficiency of the transportable crusher is reduced.